This is the main wide-field imaging/deconvolution task. It uses the wprojection method for a large field of view, can make many facets, and can include outlier fields. Several deconvolution algorithms are supported. Interactive cleaning is also supported.

For making large images (>2000 pixels on a size), see hints at the end of the descriptions. For making images larger than about 5000x5000 pixels, the available memory must be larger than 2 Gigabytes. For such images, a computer with a 64-bit operating system may be needed.

WARNING: The task widefield will be deprecated in CASA 5.4. 


Parameter descriptions


Name of all input visibility files. Default: none. Examples: vis=''; vis=['', '']


Pre-name of output images. Default: none. Examples: imagename='n5921'. If outlier fields are included, then imagename=['n5921', 'outlier1', outlier2'] and the first imagename is the wide-field image output images names are: n5921.clean, n5921.residual, n5921.model, n5921.interactive.mask


Type of selection. Default: 'mfs'. Examples: mode='channel'; options: 'mfs', channel, velocity, frequency'


Algorithm to use. Default: 'clark'; options: 'clark', 'hogbom','multiscale','entropy' Strongly advise 'clark'. 'multiscale' and 'entropy' well-tested.


Image pixel size (x,y). Default = [256,256]; Examples: imsize=[500,500], or imsize=500. Example for multiple fields: imsize=[(1000, 1000), (100, 100)]


Cell size (x,y). Default=['1arcsec,'1arcsec']. Examples: cell=['0.5arcsec,'0.5arcsec'] or cell='0.5arcsec'


Direction position or the field for the image center. A list of the above is needed for multiple-fields. Default: '' -->field='0' as center. Examples: phasecenter='6'; phasecenter='J2000 19h30m00 -40d00m00'; phasecenter=['J2000 19h30m00 -40d00m00', 'J2000 19h57m00 40d00m00'] for wide-field, plus one outlier field.


Stokes parameters to image. Default='I'. Examples: stokes='IQUV'; options: 'I','IV','IQU','IQUV'


Number iterations, set to zero for no CLEANing. Default: 500. Examples: niter=500


Loop gain for CLEANing. Default: 0.1. Examples: gain=0.1


Flux level at which to stop CLEANing (units=mJy). Default: 0.0. Examples: threshold=0.0


Name(s) of mask image(s) used for CLEANing. Default: ''. Examples: mask='orion.mask' (Number of mask fields must equal number of imaged fields)


List of [blc-x,blc-y,trc-x,trc-y] values. Default: [ ]. Examples: cleanbox=[110,110,150,145]; This can also be a filename with clean values: fieldindex blc-x blc-y trc-x trc-y; cleanbox = 'interactive' is very useful.


Data selection


Number of channels to select. Default: 1. Examples: nchan=45


Start channel, 0-indexed. Default=0. Examples: start=5; if mode='frequency' then a frequency value e.g., start='1.4GHz'


Channel width (value > 1 indicates channel averaging). Default=1. Examples: width=5; if mode='frequency' then a frequency value e.g., width='10kHz'


Step in channel number. Default=1. Examples: step=2


Select field using field id(s) or field name(s). [run listobs to obtain the list id's or names] Default: ''=all fields. If field string is a non-negative integer, it is assumed a field index otherwise, it is assumed a field name. Examples: field='0~2',field='0~, field ids 0,1,2; field='0,4,5~7', field ids 0,4,5,6,7; field='3C286,3C295', field named 3C286 and 3C295; field = '3,4C*', field id 3, all names starting with 4C; example for multiple ms in vis parameter: field=['0~2', '1,2']


Select spectral window/channels. Default: ''=all spectral windows and channels. Examples: spw='0~2,4', spectral windows 0,1,2,4 (all channels); spw='<2', spectral windows less than 2 (i.e. 0,1); spw='0:5~61', spw 0, channels 5 to 61; spw='0,10,3:3~45', spw 0,10 all channels, spw 3, channels 3 to 45; spw='0~2:2~6', spw 0,1,2 with channels 2 through 6 in each; spw='0:0~10;15~60', spectral window 0 with channels 0-10,15-60; spw='0:0~10,1:20~30,2:1;2;3', spw 0, channels 0-10, spw 1, channels 20-30, and spw 2, channels, 1,2 and 3; for multiple ms in vis parameter: spw=['0,10,3:3~45', '<2']


Select time range subset of data (not implemented yet). Default='' meaning no time selection. Examples: timerange='YYYY/MM/DD/HH:MM:SS.sss'; timerange='< YYYY/MM/DD/HH:MM:SS.sss'; timerange='> YYYY/MM/DD/HH:MM:SS.sss'; timerange='ddd/HH:MM:SS.sss'; timerange='< ddd/HH:MM:SS.sss'; timerange='> ddd/HH:MM:SS.sss'


Specify rest frequency to use for image. Default='' (i.e., try to use the restfreq specified in the visibility data).




Weighting to apply to visibilities. Default='natural'. Examples: weighting='uniform'; options: 'natural', 'uniform', 'briggs', 'briggsabs', 'radial', 'superuniform'


'briggs' and 'briggsabs' robustness parameter. Default=0.0. Examples: robust=0.5; options: -2.0 to 2.0; -2 (uniform)/+2 (natural)


Number of pixels to determine uv-cell size for weight calculation. Used with 'superuniform' or 'briggs' weighting schemes. Examples: npixels=3


Gridding method for the image. Options: 'ft' (standard interferometric gridding) or 'wproject' (wprojection algorithm for gridding). Default: 'wproject'


Number of w-projection planes to use for gridding. Default: 256. Examples: wprojplanes=64; Good value = BMAX(klambda) * Map width(arcmin)^2 / 600


Number of facets along one axis on central image. Image is divided in facets x facets rectangles. Default: 1. Examples: facets=3 makes 3x3 images to cover the field; if ftmachine = 'ft', only faceting is used; if ftmachine = 'wproject', both wplanes and faceting can be used.


Change the threshold at which the deconvolution cycle will stop and degrid and subtract from the visibilities. For bad PSFs, reconcile often (cyclefactor=4 or 5); For good PSFs, use cyclefactor 1.5 to 2.0. Default: 2.5.  Examples: cyclefactor=4, but decreases speed considerably; 


Cycle threshold doubles in this number of iterations. Default: -1. Examples: cyclespeedup=500


MEM parameters (Experimental, not well-tested)


Target image sigma. Default: '0.001Jy'. Examples: sigma='0.1Jy'


Target flux for final image. Default: '1.0Jy'. Examples: targetflux='200Jy'


Constrain image to match target flux, otherwise targetflux is used to initialize model only. Default: False. Examples: constrainflux=True


Name of MEM prior images. Default: ['']. Examples: prior='source_mem.image'


Multi-scale parameters (Experimental, not well-tested)


Stop component search when the largest scale has found this number of negative components; -1 means continue component search even if the largest component is negative. Default: 2. Examples: negcomponent=-1


Used for alg='multiscale'; set a number of scales or a vector. Default: [0,3,10]. Examples: scales=[0.0,3.0,10.0, 30]


Interactive masking


When cleanbox is set to 'interactive', this is the number of iterations between each clean to update mask interactively. However, this number can be adjusted during execution.



Apply additional uv tapering of the visibilities. Default: uvtaper=False. Examples: uvtaper=True

uvtaper=True expandable parameters


uv-taper on outer baselines in uv-plane [bmaj, bmin, bpa] taper Gaussian scale in uv or angular units. NOTE: uv taper in (klambda) is roughly on-sky FWHM(arcsec/200). Default: outertaper=[ ] (no outer taper applied). Examples: outertaper=['5klambda'] circular taper FWHM=5 kilo-lambda; outertaper=['5klambda','3klambda','45.0deg']; outertaper=['10arcsec'] on-sky FWHM 10"; outertaper=['300.0'] default units are meters in aperture plane


uv-taper in center of uv-plane. NOT YET IMPLEMENTED



Output Gaussian restoring beam for CLEAN image [bmaj, bmin, bpa] elliptical Gaussian restoring beam. Default units are in arc-seconds for bmaj,bmin, degrees for bpa.  Default: restoringbeam=[ ] use PSF calculated from dirty beam. Examples: restoringbeam=['10arcsec'] circular Gaussian FWHM 10"; restoringbeam=['10.0','5.0','45.0deg'] 10"x5" at 45 degrees


If True will create scratch columns if they are not there. And after clean completes the predicted model visibility is from the clean components are written to the MS.


Run asynchronously. Default = False. (do not run asychronously)